include ../_util-fns

:marked
  Motion is an important aspect in the design of modern web applications. Good
  user interfaces transition smoothly between states with engaging animations
  that call attention where it's needed. Well-designed animations can make a UI not only
  more fun but also easier to use.

  Angular's animation system lets you build animations that run with the same kind of native
  performance found in pure CSS animations. You can also tightly integrate your
  animation logic with the rest of your application code, for ease of control.

.alert.is-helpful
  :marked
    Angular animations are built on top of the standard [Web Animations API](https://w3c.github.io/web-animations/)
    and run natively on [browsers that support it](http://caniuse.com/#feat=web-animation).

    For other browsers, a polyfill is required. Grab
    [`web-animations.min.js` from GitHub](https://github.com/web-animations/web-animations-js) and
    add it to your page.


:marked
  # Contents

  * [Example: Transitioning between two states](#example-transitioning-between-states).
  * [States and transitions](#states-and-transitions).
  * [Example: Entering and leaving](#example-entering-and-leaving).
  * [Example: Entering and leaving from different states](#example-entering-and-leaving-from-different-states).
  * [Animatable properties and units](#animatable-properties-and-units).
  * [Automatic property calculation](#automatic-property-calculation).
  * [Animation timing](#animation-timing).
  * [Multi-step animations with keyframes](#multi-step-animations-with-keyframes).
  * [Parallel animation groups](#parallel-animation-groups).
  * [Animation callbacks](#animation-callbacks).

.l-sub-section
  :marked
      The examples in this page are available as a <live-example></live-example>.

a(id="example-transitioning-between-states")
.l-main-section
:marked
  ## Quickstart example: Transitioning between two states
figure
  img(src="/resources/images/devguide/animations/animation_basic_click.gif" alt="A simple transition animation" align="right" style="width:220px;margin-left:20px" )
:marked
  You can build a simple animation that transitions an element between two states
  driven by a model attribute.

  Animations are defined inside `@Component` metadata. Before you can add animations, you need
  to import a few animation-specific imports and functions:

+makeExample('animations/ts/src/app/app.module.ts', 'animations-module', 'app.module.ts (@NgModule imports excerpt)')(format=".")
+makeExample('animations/ts/src/app/hero-list-basic.component.ts', 'imports', 'hero-list-basic.component.ts')(format=".")

:marked
  With these, you can define an *animation trigger* called `heroState` in the component
  metadata. It uses animations to transition between two states: `active` and `inactive`. When a
  hero is active, the element appears in a slightly larger size and lighter color.

+makeExample('animations/ts/src/app/hero-list-basic.component.ts', 'animationdef', 'hero-list-basic.component.ts (@Component excerpt)')(format=".")

.alert.is-helpful
  :marked
    In this example, you are defining animation styles (color and transform) inline in the
    animation metadata.

:marked
  Now, using the `[@triggerName]` syntax, attach the animation that you just defined to
  one or more elements in the component's template.

+makeExample('animations/ts/src/app/hero-list-basic.component.ts', 'template', 'hero-list-basic.component.ts (excerpt)')(format=".")

:marked
  Here, the animation trigger applies to every element repeated by an `ngFor`. Each of
  the repeated elements animates independently. The value of the
  attribute is bound to the expression `hero.state` and is always either `active` or `inactive`.

  With this setup, an animated transition appears whenever a hero object changes state.
  Here's the full component implementation:

+makeExample('animations/ts/src/app/hero-list-basic.component.ts', '', 'hero-list-basic.component.ts')

:marked
  ## States and transitions

  Angular animations are defined as logical **states** and **transitions**
  between states.

  An animation state is a string value that you define in your application code. In the example
  above, the states `'active'` and `'inactive'` are based on the logical state of
  hero objects. The source of the state can be a simple object attribute, as it was in this case,
  or it can be a value computed in a method. The important thing is that you can read it into the
  component's template.

  You can define *styles* for each animation state:

+makeExample('animations/ts/src/app/hero-list-basic.component.ts', 'states')(format=".")

:marked
  These `state` definitions specify the *end styles* of each state.
  They are applied to the element once it has transitioned to that state, and stay
  *as long as it remains in that state*. In effect, you're defining what styles the element has in different states.

  After you define states, you can define *transitions* between the states. Each transition
  controls the timing of switching between one set of styles and the next:

+makeExample('animations/ts/src/app/hero-list-basic.component.ts', 'transitions')(format=".")

figure.image-display
  img(src="/resources/images/devguide/animations/ng_animate_transitions_inactive_active.png" alt="In Angular animations you define states and transitions between states" width="400")

:marked
  If several transitions have the same timing configuration, you can combine
  them into the same `transition` definition:

+makeExample('animations/ts/src/app/hero-list-combined-transitions.component.ts', 'transitions')(format=".")

:marked
  When both directions of a transition have the same timing, as in the previous
  example, you can use the shorthand syntax `<=>`:

+makeExample('animations/ts/src/app/hero-list-twoway.component.ts', 'transitions')(format=".")

:marked
  You can also apply a style during an animation but not keep it around
  after the animation finishes. You can define such styles inline, in the `transition`. In this example,
  the element receives one set of styles immediately and is then animated to the next.
  When the transition finishes, none of these styles are kept because they're not
  defined in a `state`.

+makeExample('animations/ts/src/app/hero-list-inline-styles.component.ts', 'transitions')(format=".")

:marked
  ### The wildcard state `*`

  The `*` ("wildcard") state matches *any* animation state. This is useful for defining styles and
  transitions that apply regardless of which state the animation is in. For example:

  * The `active => *` transition applies when the element's state changes from `active` to anything else.
  * The `* => *` transition applies when *any* change between two states takes place.

figure.image-display
  img(src="/resources/images/devguide/animations/ng_animate_transitions_inactive_active_wildcards.png" alt="The wildcard state can be used to match many different transitions at once" width="400")


:marked
  ### The `void` state

  The special state called `void` can apply to any animation. It applies
  when the element is *not* attached to a view, perhaps because it has not yet been
  added or because it has been removed. The `void` state is useful for defining enter and
  leave animations.

  For example the `* => void` transition applies when the element leaves the view,
  regardless of what state it was in before it left.

figure.image-display
  img(src="/resources/images/devguide/animations/ng_animate_transitions_void_in.png" alt="The void state can be used for enter and leave transitions" width="400")

:marked
  The wildcard state `*` also matches `void`.

  ## Example: Entering and leaving
figure
  img(src="/resources/images/devguide/animations/animation_enter_leave.gif" alt="Enter and leave animations" align="right" style="width:250px;")
:marked
  Using the `void` and `*` states you can define transitions that animate the
  entering and leaving of elements:

  * Enter: `void => *`
  * Leave: `* => void`

  For example, in the `animations` array below there are two transitions that use 
  the `void => *` and `* => void` syntax to animate the element in and out of the view.
+makeExample('animations/ts/src/app/hero-list-enter-leave.component.ts', 'animationdef', 'hero-list-enter-leave.component.ts (excerpt)')(format=".")

:marked
  Note that in this case the styles are applied to the void state directly in the
  transition definitions, and not in a separate `state(void)` definition. Thus, the transforms
  are different on enter and leave: the element enters from the left
  and leaves to the right.

.l-sub-section
  :marked
    These two common animations have their own aliases:
  code-example(language="typescript").
    transition(':enter', [ ... ]); // void => *
    transition(':leave', [ ... ]); // * => void

:marked
  ## Example: Entering and leaving from different states
figure
  img(src="/resources/images/devguide/animations/animation_enter_leave_states.gif" alt="Enter and leave animations combined with state animations" align="right" style="width:200px" )
:marked
  You can also combine this animation with the earlier state transition animation by
  using the hero state as the animation state. This lets you configure
  different transitions for entering and leaving based on what the state of the hero
  is:

  * Inactive hero enter: `void => inactive`
  * Active hero enter: `void => active`
  * Inactive hero leave: `inactive => void`
  * Active hero leave: `active => void`

  This gives you fine-grained control over each transition:

figure.image-display
  img(src="/resources/images/devguide/animations/ng_animate_transitions_inactive_active_void.png" alt="This example transitions between active, inactive, and void states" width="400")


+makeExample('animations/ts/src/app/hero-list-enter-leave-states.component.ts', 'animationdef', 'hero-list-enter-leave.component.ts (excerpt)')(format=".")

:marked
  ## Animatable properties and units

  Since Angular's animation support builds on top of Web Animations, you can animate any property
  that the browser considers *animatable*. This includes positions, sizes, transforms, colors,
  borders, and many others. The W3C maintains
  [a list of animatable properties](https://www.w3.org/TR/css3-transitions/#animatable-properties)
  on its [CSS Transitions page](https://www.w3.org/TR/css3-transitions).

  For positional properties that have a numeric value, you can define a unit by providing
  the value as a string with the appropriate suffix:

  * `'50px'`
  * `'3em'`
  * `'100%'`

  If you don't provide a unit when specifying dimension, Angular assumes the default of `px`:

  * `50` is the same as saying `'50px'`

  ## Automatic property calculation
figure
  img(src="/resources/images/devguide/animations/animation_auto.gif" alt="Animation with automated height calculation" align="right" style="width:220px;margin-left:20px" )
:marked
  Sometimes you don't know the value of a dimensional style property until runtime.
  For example, elements often have widths and heights that
  depend on their content and the screen size. These properties are often tricky
  to animate with CSS.

  In these cases, you can use a special `*` property value so that the value of the
  property is computed at runtime and then plugged into the animation.

  In this example, the leave animation takes whatever height the element has before it
  leaves and animates from that height to zero:

+makeExample('animations/ts/src/app/hero-list-auto.component.ts', 'animationdef')(format=".")

:marked
  ## Animation timing

  There are three timing properties you can tune for every animated transition:
  the duration, the delay, and the easing function. They are all combined into
  a single transition *timing string*.

  ### Duration

  The duration controls how long the animation takes to run from start to finish.
  You can define a duration in three ways:

  * As a plain number, in milliseconds: `100`
  * In a string, as milliseconds: `'100ms'`
  * In a string, as seconds: `'0.1s'`

  ### Delay

  The delay controls the length of time between the animation trigger and the beginning
  of the transition. You can define one by adding it to the same string
  following the duration. It also has the same format options as the duration:

  * Wait for 100ms and then run for 200ms: `'0.2s 100ms'`

  ### Easing

  The [easing function](http://easings.net/) controls how the animation accelerates
  and decelerates during its runtime. For example, an `ease-in` function causes
  the animation to begin relatively slowly but pick up speed as it progresses. You
  can control the easing by adding it as a *third* value in the string after the duration
  and the delay (or as the *second* value when there is no delay):

  * Wait for 100ms and then run for 200ms, with easing: `'0.2s 100ms ease-out'`
  * Run for 200ms, with easing: `'0.2s ease-in-out'`

figure
  img(src="/resources/images/devguide/animations/animation_timings.gif" alt="Animations with specific timings" align="right" style="width:220px;margin-left:20px" )
:marked
  ### Example

  Here are a couple of custom timings in action. Both enter and leave last for
  200 milliseconds, that is `0.2s`, but they have different easings. The leave begins after a
  slight delay of 10 milliseconds as specified in `'0.2s 10 ease-out'`:
  

+makeExample('animations/ts/src/app/hero-list-timings.component.ts', 'animationdef', 'hero-list-timings.component.ts (excerpt)')(format=".")

:marked
  ## Multi-step animations with keyframes
figure
  img(src="/resources/images/devguide/animations/animation_multistep.gif" alt="Animations with some bounce implemented with keyframes" align="right" style="width:220px;margin-left:20px" )
:marked
  Animation *keyframes* go beyond a simple transition to a more intricate animation
  that goes through one or more intermediate styles when transitioning between two sets of styles.

  For each keyframe, you specify an *offset* that defines at which point
  in the animation that keyframe applies. The offset is a number between zero,
  which marks the beginning of the animation, and one, which marks the end.

  This example adds some "bounce" to the enter and leave animations with
  keyframes:

+makeExample('animations/ts/src/app/hero-list-multistep.component.ts', 'animationdef', 'hero-list-multistep.component.ts (excerpt)')(format=".")

:marked
  Note that the offsets are *not* defined in terms of absolute time. They are relative
  measures from zero to one. The final timeline of the animation is based on the combination
  of keyframe offsets, duration, delay, and easing.

  Defining offsets for keyframes is optional. If you omit them, offsets with even
  spacing are automatically assigned. For example, three keyframes without predefined
  offsets receive offsets `0`, `0.5`, and `1`.

:marked
  ## Parallel animation groups
figure
  img(src="/resources/images/devguide/animations/animation_groups.gif" alt="Parallel animations with different timings, implemented with groups" align="right" style="width:220px;margin-left:20px" )
:marked
  You've seen how to animate multiple style properties at the same time:
  just put all of them into the same `style()` definition.

  But you may also want to configure different *timings* for animations that happen
  in parallel. For example, you may want to animate two CSS properties but use a
  different easing function for each one.

  For this you can use animation *groups*. In this example, using groups both on
  enter and leave allows for two different timing configurations. Both
  are applied to the same element in parallel, but run independently of each other:

+makeExample('animations/ts/src/app/hero-list-groups.component.ts', 'animationdef', 'hero-list-groups.component.ts (excerpt)')(format=".")

:marked
  One group animates the element transform and width; the other group animates the opacity.

:marked
  ## Animation callbacks

  A callback is fired when an animation is started and also when it is done.

  In the keyframes example, you have a `trigger` called `@flyInOut`. You can hook
  those callbacks like this:

+makeExample('animations/ts/src/app/hero-list-multistep.component.ts', 'template', 'hero-list-multistep.component.ts (excerpt)')(format=".")

:marked
  The callbacks receive an `AnimationEvent` that contains contains useful properties such as 
  `fromState`, `toState` and `totalTime`.

  Those callbacks will fire whether or not an animation is picked up.
